For all the rain and attention it received this year, canola was disappointing. I have heard some cases where it yielded well, but they are the outliers. Most crops seemed to get washed out and never really recovered anywhere near as well as they should. In August I wrote an article outlining the influence of the Turnip Yellows Virus and how it may be to blame for the canola woes. For my previous article on the subject, click here. Ben Congdon, an entomologist at DPIRD, upon a visit to Geraldton, said that he didn’t think there were any paddocks left in the port zone which weren’t infected. It is hard to tease out how much of the canola poor yield was from the TuYV and how much was from environmental factors. Afterall, there was compromised timing, nutrient deficiency, waterlogging etc. and aphids love sick crops. Infection from the virus has likely robbed the crops of some yield and should partly explain the disappointing yields. The risk is that this virus (TuYV) and its vectors (principally Green Peach Aphids) are now endemic in the landscape, and will wreak havoc with crops next year.

 

How to manage the TuYV?

Key points.

• Turnip Yellows Virus (TuYV) hasn’t been seen in the Geraldton port zone for around a decade, until this year.
• TuYV can hamstring crop yields. Loss estimates range from 10-50%, which seems to back up yield reports of this harvest.
• Early crop infection is much worse than later infection.
• Green Peach Aphids (GPA) are the most effective vectors for the virus.
• GPA are resistant to SP and OP (e.g. Scud, Lorsban) insecticides, necessitating the use of expensive products.
• Control GPA to keep TuYV out of the crop.
• GPA don’t necessarily have the virus, but they can collect the virus from host plants, carry it in their body, then transmit it to new plants when they migrate for feeding. If this is transmitted to a new crop, it can mean that the whole crop can be infected soon after the aphids arrive and begin feeding, reproducing, and moving throughout the crop.
• Early infections damage crop yields more than late infections.
• Monitor canola crops closely, especially early after emergence, to minimize losses next year.
• Ben Congdon, DPIRD, suggests spraying as soon as soon as GPA appear in crop. Obviously there may be some transmission, but it should stop the infection before it infects every plant in the paddock. Spray early, at the first detection.

 

GPA and the TUYV are here – now what?

They don’t innately have the virus, they must spread it from a host to new crops. Especially bad if they bring infection to the edge of the field, then they spread throughout the field. So best bet is to go hard early and kill them.

So what to do?

1. Take no prisoners when it comes to summer weeds. This will prevent over summering of GPA. The list of hosts for GPA and TuYV is extensive, so any greenery is likely to host them. Known hosts include pulses, canola/other brassicas, clovers, medics, marshmallow, and likely also others. Therefore keep the summer fallows clean and minimise the green bridge, especially volunteer/regrowth canola.

2. Research says to delay sowing to avoid early infestation of crops and then dealing with GPA for an extended season. But, early sowing is the best path to maximise canola yields. Therefore, we will need to rely on insecticides to keep the crop alive.

3. Have insecticide in the shed. My prediction is GPA will appear in crop and we will need to spray all canola where it is present across much of the port zone. This will be with products that I have scarcely recommended until 2024, so keep your supplier in the loop to get the stock.

4. Be vigilant and monitor. Aphids will generally appear on the edges of crop before moving into the rest of it. Monitor closely to check as soon as GPA are present in the crop. Keep abreast of PestFax and other agronomy chat. Once it gets found in some paddocks it won’t be far away from others.

5. Because GPA are resistant to common insecticides, we will need to use specialist aphicides. These fortunately tend to be less damaging to predatory bugs/beneficial insects so there is a silver lining.

i. Transform (Sulfoxaflor)
ii. Aria/Mainman (Flonicamid)
iii. Versys (Afidopyropen)
iv. Parachute/trump/Biopest (High grade specialist paraffinic oils)

The above all work on GPA (so far!) and its important to keep them that way. Rotate the groups and use them in the best conditions possible to ensure they continue to work. The high grade paraffinic oils (Parachute/Biopest/Trump) will likely not evolve resistance, so could be worth including as an adjuvant with sprays to stop the aphids without ‘using a shot’ of insecticide. Don’t worry, they are all expensive (~$15-20/ha) so you won’t form a habit of using them like other insecticides!

Paraffinic oils such as Biopest or Parachute have a different mode of action. Though they tend to kill all insects through their mode of action (they essentially suffocate the insects by smothering their ‘lungs’) they are not considered disruptive as the effect is not residual. Therefore they can be used with impunity without great fear of resistance developing They can even stand in as an adjuvant with some herbicide brews- check with your agronomist first.

6. Keep stubble standing where possible- burned stubble/ kelly chained stubble seem to allow aphids to colonise more readily. It’s going to be inevitable in some paddocks for trashflow reasons but where possible, it may be a 1% to keep aphids away.

7. Seed treatments likely won’t work- they belong in the 4A group to which GPA are resistant. So there is no saving grace in this respect. Although, all bought canola seed comes with Gaucho or Cruiser Opti which might save you from spraying for different pests, and therefore having to apply disruptive chemicals.

8. There does not appear to be any differences in varietal resistance. Some studies showed that there was differences in older varieties but I couldn’t pick any resistance this year. So on that note, continue to chose the best canola variety for your situation.

9. Friendly bugs. Insects that will be especially good for controlling aphids are parasitoid wasps, brown lacewings, ladybirds (the larvae are the hungry ones) and hover flies. I saw heaps of hoverflies this year in some canola crops, so hopefully they have eggs that can survive summer. Ladybugs, parasitoid wasps, and lacewings were also present to varying degrees. To this end, Versys and Aria/Mainman will be very safe to use. Transform can be hotter and can cause some damage to these species. (Source: Cesar Australia comparison table). To this end, it is worth planning on the first aphicide shot being Transform, as it will likely be used before any beneficial wasps build up. This will make it in theory less disruptive than spraying it later in the season. For reference, see the below table with highlighted rows showing the weapons in your arsenal and the columns the bugs we want to encourage in crop.

It looks like canola will be a very needy crop next year, which is a shame because there is a lot of weeds to deal with. The presence of the virus this year doesn’t mean its curtains for canola, and there will be huge benefits by keeping the crop clean. Keep your eyes peeled for GPA, as they may herald the beginning of a pandemic. Take a proactive approach to monitoring and spraying, and this might delay or prevent the infection of the canola and maximise potential yield.

 

Figure 1. A brown lacewing larvae feasting on aphids.

 

Figure 2. Ladybug larvae devouring aphids. Bad day to be an aphid.

 

Figure 3. An aphid parasitoid wasp laying an egg in an aphid. Photo: Andrew Weeks, Cesar Australia.

 

Figure 4. Hoverfly larvae skewering an aphid. Gruesome.

Further reading
https://ausveg.com.au/app/uploads/technical-insights/VG15034.pdf
https://cesaraustralia.com/wp-content/uploads/2023/05/CesarAustralia_ToxicityTable_April2024.pdf